Effects of endothelial Hif-2α deletion on tumor angiogenesis. (A) Representative CD31 staining of LLC xenograft tumors, showing decreased numbers of functional vessels (black arrowheads indicate lumenized vessels, defined as vessels with open lumens) in tumors grown in KO mice. Vessels without apparent lumens are indicated by red arrowheads. (B) Quantification of number of vessels with open lumens. (C) Representative field showing FITC-labeled vessels in LLC xenografts. (D-E) Quantification of overall vessel density (total number of vessels, proportion of lumenized vessels) and vascular area. (F) Staining for hypoxia and apoptosis using pimonidazole and Apo-BrdU DNA (TUNEL) fragmentation kit. (G-H) Quantification of pimonidazole and TUNEL stains in large (> 8 mm; G) and small (< 8 mm; H) LLC xenografts. (I) Growth curves for intradermal B16F1 melanoma xenografts in control and KO mice. (J) Weight of B16F1 xenografts harvested after 28 days. (K) SMA staining of B16F1 xenografts grown in control and KO mice, showing similar mural cell coverage. (L) Vessel density, including SMA-positive and SMA-negative vessels, in B16F1 xenografts (n = 6). *P < .05; **P < .01.